(a) Field of the Invention
The present invention relates to a Liquid Crystal Display (LCD) and a driving method thereof. More specifically, the present invention relates to an LCD and a driving method for providing compensated data voltage in order to improve a response time of the liquid crystal.
(b) Description of the Related Art
As personal computers (PCs) and televisions have recently become lighter in weight and slimmer in thickness, lighter and slimmer display devices have also been in great demand. Accordingly, flat panel type displays such as LCDs rather than cathode ray tubes (CRTS) are being developed.
In an LCD, a liquid crystal layer having anisotropic permittivity is injected between two substrates of a panel, and light transmittivity of the panel is controlled by applying and controlling an electric field to obtain desired images. An LCD is one of the most commonly used portable flat panel display devices. In particular, the thin film transistor liquid crystal display (TFT-LCD) employing the TFT as a switching element is most widely used.
As more TFT-LCDs have been used as display devices of computers and televisions, it has become increasingly important to enable display of moving pictures on the TFT-LCD. However, conventional TFT-LCDs have a relatively slow response speed, so it is difficult to enable moving pictures thereon. To solve the problem of slow response speed, a different type of TFT-LCD that uses an optically compensated band (OCB) mode or ferro-electric liquid crystal (FLC) materials has been developed.
However, the structure of the conventional TFT-LCD panel must be modified to use the OCB mode or the FLC materials. The Korean patent application No. 2000-5442 discloses a “Liquid crystal display and method thereof” to enhance the response speed of the LCD by modifying the liquid crystal driving method without modifying the structure of the TFT-LCD.
No. 2002-5442 generates a compensation data voltage by considering data voltages of present and previous frames, and provides the compensation data voltage to a data line of the LCD panel so that the pixel voltage becomes the target level immediately, and thereby the response quality is enhanced. The compensation data voltage is determined according to a dynamic capacitance and a response speed of the liquid crystal.
However, the dynamic capacitance and the response speed vary according to temperature. For example, when the temperature increases, the capacitance of liquid crystal decreases and the response speed of liquid crystal increases. Conversely, when the temperature decreases, the capacitance of the liquid crystal increases and the response speed decreases.
No. 2002-5442 compensates data voltage based on a predetermined compensation value with respect to a specific temperature, but parameters for setting the compensation value according to temperature vary as described above. Accordingly, over compensation occurs when a present temperature is higher than the specific temperature, and under compensation occurs when the present temperature is lower than the specific temperature, so correct data voltage compensation cannot be performed.
In an environment for displaying a moving picture rather than a PC graphics environment displaying a character or a still image, over-compensation of the data voltage is difficult to see, and the more the over-compensation occurs, the better the quality of the moving picture becomes.
FIG. 1 shows an example of compensating the moving picture in the prior art.
When the under compensation is performed by compensating the moving picture of a rectangular shape according to the prior art regardless of temperature, as shown in (a) of FIG. 1, a response time becomes slower than one frame time, so an afterimage occurs. When the over compensation is performed, as shown in (b) of FIG. 1, an artifact in which an edge of an object is exaggeratedly displayed occurs.
However, some viewers prefer a smooth picture that occurs when response speed of the LCD is low because of the under-compensation, and some viewers prefer an over-compensated picture in which an edge of an object is distinctly seen.
The prior art is deficient in that adaptive compensation is not performed because the data voltage is modified based on a fixed compensation voltage regardless of various parameters such as temperature, taste of a user, and environment.